The Open Group Base Specifications Issue 8
IEEE Std 1003.1-2024
Copyright © 2001-2024 The IEEE and The Open Group

NAME

pthread_rwlock_trywrlock, pthread_rwlock_wrlock — lock a read-write lock object for writing

SYNOPSIS

#include <pthread.h>

int pthread_rwlock_trywrlock(pthread_rwlock_t *
rwlock);
int pthread_rwlock_wrlock(pthread_rwlock_t *
rwlock);

DESCRIPTION

The pthread_rwlock_trywrlock() function shall apply a write lock like the pthread_rwlock_wrlock() function, with the exception that the function shall fail if any thread currently holds rwlock (for reading or writing).

The pthread_rwlock_wrlock() function shall apply a write lock to the read-write lock referenced by rwlock. The calling thread shall acquire the write lock if no thread (reader or writer) holds the read-write lock rwlock. Otherwise, if another thread holds the read-write lock rwlock, the calling thread shall block until it can acquire the lock. If a deadlock condition occurs or the calling thread already owns the read-write lock for writing or reading, the call shall either deadlock or return [EDEADLK].

Results are undefined if any of these functions are called with an uninitialized read-write lock.

If a signal is delivered to a thread waiting for a read-write lock for writing, upon return from the signal handler the thread resumes waiting for the read-write lock for writing as if it was not interrupted.

RETURN VALUE

The pthread_rwlock_trywrlock() function shall return zero if the lock for writing on the read-write lock object referenced by rwlock is acquired. Otherwise, an error number shall be returned to indicate the error.

If successful, the pthread_rwlock_wrlock() function shall return zero; otherwise, an error number shall be returned to indicate the error.

ERRORS

The pthread_rwlock_trywrlock() function shall fail if:

[EBUSY]
The read-write lock could not be acquired for writing because it was already locked for reading or writing.

The pthread_rwlock_wrlock() function may fail if:

[EDEADLK]
A deadlock condition was detected or the current thread already owns the read-write lock for writing or reading.

These functions shall not return an error code of [EINTR].


The following sections are informative.

EXAMPLES

None.

APPLICATION USAGE

Applications using these functions may be subject to priority inversion, as discussed in XBD 3.275 Priority Inversion .

RATIONALE

If an implementation detects that the value specified by the rwlock argument to pthread_rwlock_trywrlock() or pthread_rwlock_wrlock() does not refer to an initialized read-write lock object, it is recommended that the function should fail and report an [EINVAL] error.

FUTURE DIRECTIONS

None.

SEE ALSO

pthread_rwlock_clockrdlock , pthread_rwlock_clockwrlock , pthread_rwlock_destroy , pthread_rwlock_rdlock , pthread_rwlock_unlock

XBD 3.275 Priority Inversion , 4.15.2 Memory Synchronization , <pthread.h>

CHANGE HISTORY

First released in Issue 5.

Issue 6

The following changes are made for alignment with IEEE Std 1003.1j-2000:

IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/104 is applied, updating the ERRORS section so that the [EDEADLK] error includes detection of a deadlock condition.

Issue 7

The pthread_rwlock_trywrlock() and pthread_rwlock_wrlock() functions are moved from the Threads option to the Base.

The [EINVAL] error for an uninitialized read-write lock object is removed; this condition results in undefined behavior.

POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0290 [720] and XSH/TC2-2008/0291 [722] are applied.

End of informative text.

 

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